This invention relates to repair of a strip of material bonded to an article surface, and more particularly, in one form, to the repair of a strip of wear resistant material bonded to the surface of a gas turbine engine blade.
The manufacture of gas turbine engine blades includes manufacture of composite blades incorporating fibrous or filament type materials, typically including a matrix and a reinforcing material. Cooler operating blades in such an engine include fan or compressor blades frequently made of stacked or laid-up plies of a reinforced polymeric material. Such blades are described in a variety of publications including U.S. Pat. No. 3,883,267--Baudier et al., patented May 13, 1975; and 5,573,377--Bond et al., patented Nov. 12, 1996.
The surface of certain composite blades is relatively soft compared with a metal surface with which it might interact. Therefore, it has been a practice to bond a wear resistant material to a composite blade surface which is subject to a rubbing or fretting type wear as a result of contact with a cooperating member during engine operation. One form of wear resistant material used in a gas turbine engine is a low friction wear coat on the dovetail of a composite blade as shown at 38 in FIGS. 4 and 5 of the above identified Bond et al. patent. Another type of such a wear resistant material is in the form of a strip of material, such as pre-impregnated Class and Teflon fiber hybrid cloth, bonded with an adhesive to composite blade surfaces as the dovetail, airfoil, etc. Such a wear strip has various edges which can be damaged, including a lengthwise edge, end edges, the edge of a corner at the juncture of a lengthwise edge and an end edge, etc. Such damage can result from operation, mishandling, etc., which has caused fraying or loosening of fibers of the strip, or disbonding of the adhesive bonding the wear strip to the blade surface.
A current practice specifies complete removal of a damaged wear strip and its adhesive, followed by replacement of the strip using a curing cycle at about 300.degree. F. and the application of pressure, for example in an autoclave. Removal of the entire wear strip and complete replacement by processing at such a temperature and pressure is time consuming and requires use of relatively costly apparatus, adding to the cost of repair. However, frequently damage to the wear strip is in a relatively small area and is localized, for example a discrete disbanding or fraying of a portion along a lengthwise edge of the wear strip.